1. Field of the Invention
The present invention generally relates to a rotary printing press for printing on sheets of printing stock. Such a printing press will typically have cylinders mounted therein, such as the plate cylinder, blanket cylinder, sheet drum and sheet transfer cylinders. The sheets of printing stock therefore need to be conveyed or transferred about the cylinders from the sheet supply source to the stacking device for stacking printed sheets. In this regard, the present invention more particularly relates to a gripper device of a rotary printing press, for conveying the sheets of printing stock on the outer cylindrical surface of the cylinders of the printing press. Such a gripping device can generally have gripper fingers which can be pivot-mounted with the cylinder, and which can cooperate with a gripper pad disposed on the cylinder. These gripper fingers can typically be controlled according to the sheet sequence of the printing run being performed.
2. Background Information
Such gripper devices are generally used to convey individual sheets of printing stock, or sheet layers, and therefore, need to be controlled according to the sheet sequence, with the control periods being timed so as to be substantially very short. Conventional gripper devices are typically equipped with relatively long grippers mounted on gripper shafts. The gripper shafts are, in turn, moved by control cams via cam rolls. The mass of the grippers, in combination with their holding devices and the gripper shaft, generally permits only a certain maximum machine speed before the cam roll would essentially permanently move away from the control cam, and thereby no longer grip sheets to be transferred. Due to the long lever arm of the grippers and the required holding forces for gripping a sheet of printing stock, grippers and holding devices generally need to be of stable design and thus tend to be heavy, which also has a limiting effect on the machine speed. Furthermore, since springs are generally used to hold the control cams in contact with the cam rolls, it has been determined that it is essentially not possible to increase the spring forces to an unlimited extent in order to press the cam roll into contact with the control cam, which contact will therefore decrease as a result of the wear and tear of the camming components.